Finishing grinding stone



Patented Feb. 7, 1928.

UNITED STATES ERNEST I. MARS, OF CHICAGO, ILLINOIS.

r'rnrsnrne GRINDING stronn. 7

No Drawing.

My invention relates to artificial stones for abrasive and polishingpurposes. Viewed in its general objects, my invention aims to provide acomposition stone for this purpose which can easily be manufactured witha highly uniform distribution of the abrasive ingredient, or of bothabrasive and polishing ingredients; which will require no poisonousingredients for its manufacture;

10 and in which the relative proportion and hardness of the abrasive andpolishing ingradients can readily be varied according to the material onwhich the stone is to be used.

16 My invention also provides a composition 7 for this purpose in whichthe body material (namely the material that has the abrasive andpolishing ingredients distributed through it) can be varied considerablyin 20 its own hardness; and in which this body material will graduallywear away to form a suitable muck when the stone is used for Wetgrinding, so that this muck can carry off the abraded particles of thematerial 2 which is being ground; and in which this body material issomewhat abrasive and is of such a nature that the detached particles ofthe object on'which the stone is used will not adhere to this'material.

In its immediate commercial aspects, my

invention is particularly suited for the manufacture of stones to beused in the last step of the grinding of the copper printing cylindersemployed on multicolor printing presses,

such as the so called rotogravure presses. Hence I am describing myinvention 'more particularly with the ingredients proportioned for thatpurpose, although I do not wish to be limited to these particular pro-40 portions or to the abrasive and polishing ingredients hereafterspecifically mentioned. Owing to the high cost of such a copper printingcylinder, it is customary to use the cylinder repeatedly for differentimprintings by grinding off the raised printing surface and againetching anew surface on it. For this purpose, the raised portions arefirst ground off by comparatively rough abrasive means, after which thecylinder is subjected to a finish-grinding; To insure a uniform diameterand a freedom from scratches, it is important that the abrasiveingredients in the stone employed for this finish-grinding shouldbedistributed through the stone is with highdegree of uniformity,thatthe' body material be uniform in hardness Application filed March18, 1927. Serial No. 176,581.

not to wear irregularly, that the stone be free from hard spots andunduly hard abrasive portio'nswhich would produce scratches,

and also that the detached particles of copper will not attachthemselves to the stone. N 0 natural stone has yet been found to meetthese severe requirements, and even the grinding stones imported forthis purpose require a good deal of subsequent hand labor for removingscratches. natural abrasive stones do not attord a sufiicient polishingfor the cylinders, so that considerable later hand labor is alsoneededto finish this polishing.

In experimenting with various possible body materials for carrying theneeded abrasive and polishing materials, I havediscovered magnesiacements to be superior to all materials previously suggested for thesame purpose, namely cements composed of magnesium carbonate or oxide,combined with magnesium chloride. I have also found that the impuritiesfound in commercial magnesite (which contains approximately'70 percentof magnesium salts and approximately.

5 percent of water) will not interfere with the use ofordinarymag'nesite asthis body material, thereby considerably reducingthe cost of the stone. Furthermore, I have found'that by employing asuitable proper-- tion of another salt of magnesium, namely magnesiumsulphate (which is commercially available under the name of Epsomsalts), I can retard the drying of the magnesia cement so as to increasethe hardness of the resulting stone to such adegree that the detachedparticles of copper will not imbed themselves into it. p g V Inmanufacturing, a finish-grinding and polishing stone for use on copperprinting plates, I have found the following proportions satisfactory:magnesite 40 ounces, crocus 48 ounces, jewelers rouge 8 ounces, Epsomsalt 8 ounces, magnesium chloride 16'ounces, water 3 pints.

Moreover, the

The magnesite, crocus and rouge are first h sifted separately throughscreens (desirably 300 mesh) and then thoroughlymixed while dry, whilethe magnesium chloride and the Epsom salts are dissolved in the water toform a solution. The mixture of the sifted dry ingredients is thenworked up with this solution to a mass of uniform consistency,

, which is forced through a screen (desirably of about;50 f mesh, forbreaking lumps and subdividing the plastic evenly) hering to it.

into a bronze mold Y which has previously been waxed to prevent the massfrom ad- Left exposed to the air at ordinary temperatures, this plasticmass hardens in from 24: to 30 hours to form the desired stone.

In the finished stone, the abrasive (crocus) and the polishingingredient (rouge) form nearly one half of the entire weight, or aboutdouble the proportion of the active ingredients in artificial stonesheretofor rov osed for the same ur 3056 so that P P l my'stone isunusually eiiicientin proportion to its weight and size. Moreover, themag nesia cement when thus diluted by the abrasive ingredient is initself an abrasive of a degree of hardness suitable for having agrinding action on copper, thereby increasing the effectiveness of mystone,

in using such a stone for wet grinding, I. have, found that the surfacewears 'evenlen.

and that the water and the grinding pol.- tions of the body materialform the so.- called muck in adesired consistency for carrying off thedetached particles of copper. I have also found that any marks still,left in the copper (if any) are so fine as to require only a quite smallamount of hand polishing to remove them. Moreaver, no poisonousmaterials are employed in the manufacture of my stone, so that Ieliminate the danger heretofore encountered in making such stones withlitharge as an ingrec'li'ent ofthe body material. 7

However, I do not wish to be limited to the above mentioned proportionsof the various ingredients or to the above recited protedure in themanufacture of my stones, since changes might obviously be made withoutdeparting from the spirit of my invention and from the appended claims.Nor do I wish to be limited to the crocus as the abrasive or to rouge asthe polishing ingredient when such an ingredient is also employed, or tothe use, of the stones of my invention for grinding copper.

For example, the degree of fineness of the resaaas (such as Epsom salt)used with it, thereby correspondingly modifying the grinding action ofthis body material and also adapting this material to prevent theadhering of detached particles harder than the copper of the usualprinting plates.

' I claim as my invention:

1. A stone for griding and polishing copper, comprising a hardened andabrasive cement softer than copper and uniformly impregnated with afinely powdered abrasive andv finely powdered rouge, the abrasive beingharder than copper, the total weight of the, abrasive and rouge beingmore than forty per cent of the weight of the. stone.

2. A. grinding stone comprising the hard ened product of an intimatemixture of a magnesia salt or salts, a finely divided abra= sive and afinely divided polishing material, with an aqueous solution of magnesiumchloride mixed with a relatively small proportion of magnesium sulphate.

A grindingstone comprising a magnesia cement hardened under theinfluence of a retarder and uniformly impregnated with a mixture offinely ground crocus and rouge, the proportion of the orocus to therouge being about eight to one, and the total weight of the crocus androuge being more than forty percent of the weight of the stone.

i. A grinding stonecomprising the product resulting from the hardeningof the plastic mass produced by intern tingling the followingingredients in approximately the proportions recited, namely: 40 ouncesmagnesite, e8 ounces crocus, 8 ounces jewelers rouge, 8 ounces Epsomsalts, 16 ounces magnesium chloride and 3 pints water.

Signed at Chicago, Illinois, March 16th.

ERNEST P. MARS.

